ly in the waters of the locality. It was noted that the flowers 

 were frequently close pollinated in the bud, and the writer (1) 

 published a brief account outlining in a general way the observed 

 facts. 



Subsequent study has shown that this species in our region is 

 regularly cleistogamous. Under certain restricted conditions the 

 flowers may open at the surface of the water, but in all observed 

 cases these also have pollen tubes entering the style when the 

 flowers open. Moreover nearly all the flowers produced on plants 

 growing under favorable conditions for vegetative growth are so 

 deeply submersed that it is impossible for the stigmas to reach 

 the surface. Yet under all circumstances seeds are developed 

 abundantly through cleistogamous fertilization. 



Darv^dn (2) argues that cases similar to this should not be 

 included under cleistogamy. He says (Chapter VIII) that the 

 flowers of Ranunculus aquatilis and Alisma nutans, for example, 

 "remain closely shut as long as they are submerged, and in this 

 condition fertilise themselves. They behave in this manner, ap- 

 parently as a protection to their pollen, and produce open flowers 

 when exposed to the air ; so that these cases seem rather different 

 from those of true cleistogamous flowers, and have not been in- 

 cluded in the list. ' ' The writer feels that the case of Hetera/)i- 

 thera dubia is quite different in that the opening of the flower, 

 when it does occur, reveals an antecedent close pollination. The 

 species seem therefore to have practically abandoned the chasmo- 

 gamic habit and should be classed as cleistogamous even though 

 it may not have the reduced or dimorphic flowers. 



Heter anther a dubia grows luxuriantly rooted at the bottom of 

 shallow, quiet water. While it is but sparingly present on ex- 

 posed shores of larger lakes it thrives in protected bays, ponds, 

 sloughs, etc., and in such habitats often dominates considerable 

 areas. Since these plants are limited to water of perhaps one 

 meter in depth it is evident that they face a double danger. 

 There is the possibility, on the one hand of becoming too deeply 

 submerged as a result of floods, and the probability, on the other 

 hand, of being stranded through the lowering of the water level 

 during the drier months of the summer. Occasionally plants 

 are found growing on mud, but these are dwarfed to a few centi- 

 meters in height whereas under optimum conditions the plant 

 is a yard long. 



49 



